1. Field of the Invention
This invention relates to techniques for minimizing the evaporative losses of stored hydrocarbons. In particular, the present invention is concerned with suppressing the volatilization of hydrocarbons contained in petroleum products such as crude oil.
2. Background of the Invention
In the past, petroleum products, particularly crude oil, have been relatively inexpensive commodities. In very recent years, however, increased world demand for all natural resources has significantly altered the prior supply/demand relationships so that losses of hydrocarbons from evaporation is deemed quite serious from an economic point of view. Moreoever, there is a concern for preserving not only petroleum hydrocarbons but all volatile liquids.
Important also is the need to protect the environment from contamination by volatile hydrocarbons. Indeed, increased world use of petroleum products has increased the needs for improvements in suppressing the loss of hydrocarbons into the atmosphere, etc.
In the description to follow, reference will be made primarily to suppressing the loss of hydrocarbons by vaporization from crude oils; however, it is to be understood that crude oil is merely one example of a hydrocarbon which contains sufficient amounts of volatile components which will undergo vaporization in substantial amounts during storage.
As will be appreciated, crude oil contains a very wide spectrum of hydrocarbons ranging from those which have very high boiling points to those which would exist in the vapor state if they were isolated. Indeed, it is the presence of these latter materials that contributes to the significant vapor pressure of crude oil.
There have been a number of techniques suggested in the past for inhibiting the vaporization of hydrocarbons. For example, in U.S. Pat. No. 1,985,491, it is suggested that a fatty acid soap be mixed with water and then beat into a froth with a vigorous air blast. The froth, thereafter, is spread on the surface of oil, so as to minimize evaporation and oxidation of the oil.
In U.S. Pat. No. 2,822,238, evaporation of volatile nonaqueous liquid products is retarded by floating small hollow particles, wet by water, on the surface of the volatile liquid.
In U.S. Pat. No. 2,907,627, a technique is disclosed for inhibiting vapor loss by spreading a synthetic resin plastic such as a polyurethane on the surface of the crude petroleum. In contrast thereto, U.S. Pat. No. 3,421,838 discloses the use of rubber cement as a vapor barrier for volatile petroleum products.
Other techniques suggested for inhibiting vaporization of hydrocarbon materials include the use of a gelling material to create an integral roof on an oil tank. In this regard, see U.S. Pat. No. 3,639,258. Mention should be made also of the technique of preventing hydrocarbon losses during the loading of vessels by use of an aqueous foam which is stable during the period corresponding to that required for loading. For this technique, see U.S. Pat. No. 3,850,206. The last two techniques for inhibiting vaporization of hydrocarbons have more limited applicability than the above-mentioned techniques.
In U.S. Application Ser. No. 702,692, filed July 6, 1976, and incorporated herein by reference, there is disclosed a very effective composition for inhibiting vapor losses of stored hydrocarbons which comprises a mixture of a surfactant and a polyglycol. This composition, when applied to the surface of a body of hydrocarbon liquid, forms an effective film type barrier thereby reducing vapor loss. Notwithstanding the significant utility of such composition in reducing vapor loss of hydrocarbons, the search for even more effective and more economic techniques for conserving natural resources and protecting the environment continue.